Liquid crystal display device and electronic apparatus

ABSTRACT

The invention can provide a liquid crystal display device in which a homeotropic alignment liquid crystal layer is interposed between a pair of substrates and a transmissive display region and a reflective display region are provided in one dotregion. A liquid crystal layer thickness-adjusting layer for making the thickness of the liquid crystal layer in the reflective display region smaller than the thickness of the liquid crystal layer in the transmissive display region can be formed between at least one substrate of the pair of substrates and the liquid crystal layer, and wherein, in at least one substrate of the pair of substrates, convex portions that protrude from the internal surface of the substrate to the inside of the liquid crystal layer are formed in the transmissive display region in the dot region and in the region where the liquid crystal layer thickness-adjusting layer is formed outside the dot region. Accordingly, the invention can provide a liquid crystal display device capable of displaying images with a wide angle in both of transmissive display and reflective display.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention relates to a liquid crystal display device and anelectronic apparatus. More specifically, the invention is related totechnology for obtaining a wide viewing angle in a liquid crystaldisplay device using a homeotropic alignment liquid crystal.

2. Description of Related Art

Transflective liquid crystal display devices which include a reflectivemode and a transmissive mode are known. In a transflective liquidcrystal display device, a liquid crystal layer is interposed between anupper substrate and a lower substrate. A reflecting film with a lighttransmissive window in a metal film such as aluminum is provided on theinternal surface of the lower substrate. The reflecting film functionsas a transflective sheet. In this case, in the reflective mode, externallight incident from the upper substrate is reflected from the reflectingfilm on the internal surface of the lower substrate after passingthrough the liquid crystal layer, then passes through the liquid crystallayer again and is emitted from the upper substrate to contribute todisplay. On the other hand, in the transmissive mode, the light from abacklight incident from the lower substrate passes through the liquidcrystal layer through the window of the reflecting film and is emittedfrom the upper substrate to the outside to contribute to the display.Therefore, the region of the reflecting film with the window is thetransmissive display region and the other region is the reflectivedisplay region.

In conventional transflective liquid crystal devices, the viewing anglein transmissive display is narrow. This is because, since atransflective sheet is provided on the internal surface of a liquidcrystal cell so that parallax is not generated, only one polarizerprovided on an observer side works on the reflective display and thedegree of freedom of optical design is small. Therefore, in order tosolve this problem, Jisaki et al. suggested a new liquid crystal displaydevice using a homeotropic alignment liquid crystal in “Development oftransflective LCD for high contrast and wide viewing angle by usinghomeotropic alignment”, M. Jisaki et al., Asia Display/IDW'01, P.133–136 (2001) cited below. The liquid crystal display device has thefollowing three characteristics:

(1) A vertical alignment (VA) mode, in which liquid crystal moleculeswith negative dielectric anisotropy are vertically aligned on asubstrate and the liquid crystals fall by applying a voltage.

(2) A “multi-gap structure” is adopted, in which the thickness (a cellgap) of the liquid crystal layer in the transmissive display region isdifferent from that of the liquid crystal layer in the reflectivedisplay region (with respect to this point, refer to Japanese UnexaminedPatent Application Publication No. 11-242226).

(3) The transmissive display region is an octagon and protrusions areprovided in the middle of the transmissive display region on a countersubstrate so that the liquid crystal molecules fall in eight directionsin the region.

See also, generally, Japanese Unexamined Patent Application PublicationNo. 2002-350853.

SUMMARY OF THE INVENTION

It is very effective to include the multi-tap structure like the onedescribed above in the transflective liquid crystal display device whenthe electro-optical characteristics (transmittance-voltagecharacteristics and reflectance-voltage characteristics) of thetransmissive display region are adjusted to those of the reflectivedisplay region. This is because light passes through the liquid crystallayer only once in the transmissive display region but twice in thereflective display region.

When the multi-gap structure is adopted and the directions in which theliquid crystal molecules fall are controlled by using the protrusionsmentioned above, for example, when spacers for regulating the thicknessof the liquid crystal layer are provided, the spacers float in thetransmissive display region where the thickness of the liquid crystallayer is large or the thickness of the liquid crystal layer must bedesigned in consideration of the height of the protrusions and the sizeof the spacers, which makes the structure complicated. That is, in themulti-gap structure liquid crystal display device which uses protrusionsfor regulating the directions in which the liquid crystal moleculesfall, effort is required to design the thickness of the liquid crystallayer and since the thickness of the liquid crystal layer stronglyaffects the display characteristics, errors generated in the design ofthe thickness of the liquid crystal layer may cause an inferior display.

It is an object of the invention to provide a homeotropic alignmenttransflective liquid crystal display device capable of displaying imageswith a wide viewing angle and having a structure more suitable forregulating the thickness (the distance between substrates, that is, acell gap) of a liquid crystal layer. It is another object of theinvention to provide a reliable liquid crystal display device whosestructure is simplified, thus improving the manufacturing efficiency andreducing the occurrence of inferior quality. It is still another objectof the present invention to provide a reliable electronic apparatuscomprising the above-mentioned liquid crystal display device.

The invention can provide a liquid crystal display device in which aliquid crystal layer is interposed between a pair of substrates and atransmissive display region and a reflective display region are providedin one dot region. The liquid crystal layer can be made of liquidcrystal with negative dielectric anisotropy that is vertically alignedin an initial state. A liquid crystal layer thickness-adjusting layerfor making the thickness of the liquid crystal layer in the reflectivedisplay region smaller than the thickness of the liquid crystal layer inthe transmissive display region is formed between at least one substrateof the pair of substrates and the liquid crystal layer, and wherein, inat least one substrate of the pair of substrates, convex portions thatprotrude from the internal surface of the substrate to the inside of theliquid crystal layer are formed in the transmissive display region inthe dot region and in the region where the liquid crystal layerthickness-adjusting layer is formed outside the dot region.

The liquid crystal display device according to the invention can beobtained by combining liquid crystal in a vertical alignment mode with atransflective liquid crystal display device and by adding a liquidcrystal layer thickness-adjusting layer (that is, a multi-gap structure)to the transflective liquid crystal display device for makingbirefringence retardation of a reflective display region almost equal tothat of a transmissive display region and it has structures forpreferably controlling the directions of the alignment of liquid crystalmolecules and preferably regulating the thickness of the liquid crystallayer in place of spacers.

In other words, according to the liquid crystal display device in thevertical alignment mode, liquid crystal molecules that are verticallyerect with respect to the substrate in an initial state fall by applyingan electric field. When nothing is designed (when pre-tilt is notgiven), the directions in which the liquid crystal molecules fall cannotbe controlled and disorder (disclinations) in the alignment is causedwhich generates display problems such as light leakage and deterioratesdisplay quality. Therefore, when a vertical alignment mode is employed,control of the directions in which the liquid crystal molecules arealigned when the electric field is applied is an important factor.

Therefore, in the liquid crystal display device according to theinvention, a convex portion is formed in at least the transmissivedisplay region of a dot region. The directions in which the liquidcrystal molecules are aligned in the region are regulated.

According to such alignment regulation, the liquid crystal molecules arevertically aligned in an initial state and have pre-tilt according tothe shape of the convex portion. As a result, it is possible to regulateor control the directions in which the liquid crystal molecules fall inthe dot region. Therefore, it is difficult to cause the disorder(disclinations) in the alignment and it is possible to avoid theinferiority in the display such as light leakage. As a result, it ispossible to reduce problems, such as after images and spots, and providea liquid crystal display device with a wide viewing angle. Also,according to the invention, the convex portion is provided in thetransmissive display region in the dot region. This is because theluminosity of the transmissive display is higher than that of thereflective display. The convex portion may be formed in each of thereflective display region and the transmissive display regions.

According to the invention, the convex portion can be formed not only inthe transmissive display region in order to regulate the alignment ofthe liquid crystal molecules, but also outside the dot region.Accordingly, it is possible to regulate the directions in which theliquid crystal molecules fall outside the dot region. Therefore, it ispossible to prevent alignment inferiority in the liquid crystalmolecules in the dot region due to the inferiority in the alignment,which is generated outside the dot region. Furthermore, since the convexportion outside the dot region is formed in the region where a liquidcrystal layer thickness-adjusting layer is arranged, it is possible touse the convex portion outside the dot region as a means for adjustingthe thickness (the distance between the substrates (hereinafter, it isreferred to as the cell gap)) of the liquid crystal layer. That is,since the thickness of the liquid crystal layer is small in the regionwhere the liquid crystal layer thickness-adjusting layer is formed, itis possible to use the convex portion as a liquid crystal layerthickness-regulating device for maintaining the cell gap at apredetermined thickness. As mentioned above, the liquid crystal displaydevice according to the invention includes a structure for regulatingthe directions in which the liquid crystal molecules fall. At the sametime, at least one of the devices for regulating the directions in whichthe liquid crystal molecules fall includes a function of regulating thecell gap. Therefore, it is not necessary to provide additional spacersas is conventionally done. As a result, it is possible to prevent thespacers from floating in the transmissive display region where thethickness of the liquid crystal layer is relatively large. Also,according to the invention, for example, the internal surface side ofthe substrate means the liquid crystal layer side of the substrate. Thatthe convex portion protrudes above the substrate means that the convexportion protrudes from the internal surface of the liquid crystal layerthickness-adjusting layer when the liquid crystal layerthickness-adjusting layer can be formed on the internal surface of thesubstrate.

Also, there can be provided a liquid crystal display device in which aliquid crystal layer that is interposed between a pair of substrates anda transmissive display region and a reflective display region areprovided in one dot region, wherein the liquid crystal layer is made ofliquid crystal with negative dielectric anisotropy that is verticallyaligned in an initial state, wherein a liquid crystal layerthickness-adjusting layer for making the thickness of the liquid crystallayer in the reflective display region smaller than the thickness of theliquid crystal layer in the transmissive display region is formedbetween at least one substrate of the pair of substrates and the liquidcrystal layer, and wherein, in at least one substrate of the pair ofsubstrates, convex portions that protrude from the internal surface ofthe substrate to the inside of the liquid crystal layer are formed inthe transmissive display region and the reflective display region in thedot region. In accordance with such a liquid crystal display device, thedirections in which the liquid crystal molecules fall are preferablyregulated by the convex portion like in the above-mentioned structure.Furthermore, the convex portion formed in the reflective display regionwhere the thickness of the liquid crystal layer is small can be used asthe means for regulating the cell gap.

In the liquid crystal display device according to the invention, each ofthe heights of the convex portions is almost equal to the thickness ofthe liquid crystal layer in the reflective display region. According tothe invention, the thickness of the liquid crystal layer of thereflective display region is small since the multi-gap structure isemployed. Therefore, it is possible to use the convex portion as themeans for regulating the cell gap by forming the convex portion to havethe height almost equal to the thickness of the liquid crystal layer ofthe reflective display region. Also, the convex portions have surfacesinclined at a predetermined angle with respect to the surfaces of thesubstrate for interposing the liquid crystal layer therebetween. It ispossible to regulate the directions in which the liquid crystalmolecules fall along the tilted surface by including the tiltedsurfaces.

Also, in the liquid crystal display device according to the invention,electrodes for driving the liquid crystal are provided on the liquidcrystal layer sides of the pair of substrates, and the convex portionsare formed on at least one electrode of the electrodes facing the liquidcrystal layer. In this case, an alignment film for vertically aligningthe liquid crystal is formed on the convex portions and the internalsurface side of the liquid crystal layer of the electrode. Also,circular polarizers for making circularly polarized light incident onthe liquid crystal layer are provided on the sides of the pair ofsubstrates opposite to the liquid crystal layer, respectively. Thecircular polarizer may be obtained by composing a polarization layerwith a retardation layer.

Furthermore, in the liquid crystal display device according to theinvention, an upper substrate and a lower substrate are provided as thepair of substrates, a backlight for transmissive display is provided onthe side of the lower substrate opposite to the liquid crystal layer,and a reflective layer selectively formed in the reflective displayregion is formed on the side of the lower substrate facing the liquidcrystal layer. In this case, it is possible to use the light from thebacklight, which is incident from the lower substrate, for thetransmissive display and to reflect external light such as illuminationand solar light incident from the upper substrate in the reflectivelayer to thus be used for the reflective display.

Also, the convex portion formed in the transmissive display region andthe convex portion formed outside the dot region or the convex portionformed in the reflective display region are preferably formed in thesame process in order to improve the manufacturing efficiency. In thiscase, the respective convex portions are made of the same material tothus easily make the respective convex portions have almost equalheight.

An electronic apparatus according to the invention can include theabove-mentioned liquid crystal display device. Such an electronicapparatus can operate in the transmissive mode and the reflective mode.Therefore, it is possible to provide an electronic apparatus having adisplay in which images can be displayed with a wide viewing angle inboth of the display modes.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numerals reference like elements, and wherein:

FIG. 1 is an equivalent circuit diagram of a liquid crystal displaydevice according to a first embodiment;

FIG. 2 is a plan view illustrating the structure of the electrodes ofthe liquid crystal display device of FIG. 1;

FIG. 3 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of the liquid crystal displaydevice of FIG. 1;

FIG. 4 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of a liquid crystal displaydevice according to a second embodiment;

FIG. 5 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of a liquid crystal displaydevice according to a third embodiment;

FIG. 6 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of a modification of the liquidcrystal display device according to the third embodiment;

FIG. 7 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of a liquid crystal displaydevice according to a fourth embodiment;

FIG. 8 is a plan schematic view and a sectional schematic viewillustrating the enlarged main portion of a liquid crystal displaydevice according to a fifth embodiment; and

FIG. 9 is a perspective view illustrating an example of an electronicapparatus according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments of the invention will now be further describedwith reference to the drawings. In the drawings, it should be understoodthat the thickness of individual layers and regions are exaggerated forclarity.

A liquid crystal display device according to an embodiment of theinvention is an active matrix liquid crystal display device using a thinfilm diode (TFD) as a switching element, in particular, a transflectiveliquid crystal display device capable of performing reflective andtransmissive display.

FIG. 1 is an equivalent circuit diagram of a liquid crystal displaydevice 100 according to the embodiment. The liquid crystal displaydevice 100 can include a scanning signal driving circuit 110 and a datasignal driving circuit 120. Signal lines, that is, a plurality ofscanning lines 13 and a plurality of data lines 9 that cross thescanning lines 13 are provided in the liquid crystal display device 100.The scanning lines 13 are driven by the scanning signal driving circuit110. The data lines 9 are driven by the data signal driving circuit 120.In the respective pixel regions 150, TFD elements 40 are seriallyconnected to liquid crystal display components (liquid crystal layers)160 between the scanning lines 13 and the data lines 9. On the otherhand, in FIG. 1, the TFD elements 40 are connected to the scanning lines13 and the liquid crystal display elements 160 are connected to the datalines 9. However, on the contrary, the TFD elements 40 may be connectedto the data lines 9 and the liquid crystal display components 160 may beconnected to the scanning lines 13.

Hereinafter, with reference to FIG. 2, the planar structure of theelectrodes included in the liquid crystal display device according tothe embodiment will now be described. As illustrated in FIG. 2, in theliquid crystal display device according to the embodiment, pixelelectrodes 31 which is rectangular in plan view are connected to thescanning lines 13 via the TFD elements 40 are provided in a matrix andthe rectangular common electrodes 9 (in a stripe) are provided to facethe pixel electrodes 31 in a direction vertical to the plane of thedrawing. The common electrodes 9 are composed of the data lines andcross the scanning lines 13 in strips. According to the embodiment, eachregion in which each of the pixel electrodes 31 is formed constitutesone dot region, and images can be displayed in each of the dot regionsarranged in a matrix.

Here, the TFD elements 40 are switching elements for connecting thescanning lines 13 to the pixel electrodes 31. The TFD elements 40 havean MIM structure in which a first conductive film using Ta as a maincomponent, an insulating film formed on the surface of the firstconductive film and using Ta₂O₃ as a main component, and a secondconductive film formed on the surface of the insulating film and usingCr as a main component are provided. The first conductive films of theTFD elements 40 are connected to the scanning lines 13 so that thesecond conductive films are connected to the pixel electrodes 31.

Next, the pixel structure of the liquid crystal display device 100according to the embodiment will now be described with reference to FIG.3. FIG. 3( a) is a schematic view illustrating the pixel structure ofthe liquid crystal display device 100, in particular, the planarstructure of the pixel electrode 31. FIG. 3( b) is a schematic viewtaken along the line A–A′ of FIG. 3( a). As illustrated in FIG. 2, theliquid crystal display device 100 according to the embodiment has thedot regions including the pixel electrodes 31 in the regions surroundedby the data lines 9 and the scanning lines 13. In the dot regions, asillustrated in FIG. 3( a), a colored layer of one of three primarycolors is arranged corresponding to one dot region. The three dotregions D1, D2, and D3 form a pixel including colored layers 22B (blue),22G (green), and 22R (red).

On the other hand, as illustrated in FIG. 3( b), in the liquid crystaldisplay device 100 according to the embodiment, liquid crystal whosemolecules are vertically aligned in an initial state, that is, a liquidcrystal layer 50 made of a liquid crystal material whose dielectricanisotropy is negative, is interposed between an upper substrate (anelement substrate) 25 and a lower substrate (a counter substrate) 10arranged to face the upper substrate.

The lower substrate 10 has a structure in which a reflecting film 20made of a metal film having a high reflectance, such as aluminum orsilver, is partially formed on the surface of a substrate main body 10Amade of a light transmissive material such as quartz or glass, with aninsulating film 24 therebetween. Here, the region in which thereflecting film 20 is formed constitutes a reflective display region R.The region in which the reflecting film 20 is not formed, that is, theregion inside an aperture 21 of the reflecting film 20, is atransmissive display region T. As mentioned above, the liquid crystaldisplay device according to the embodiment can be a vertical alignmentliquid crystal display device including the vertical alignment liquidcrystal layer 50 and is a transflective liquid crystal display devicecapable of displaying images in a reflective mode and in a transmissivemode.

The insulating film 24 formed on the substrate main body 10A has aconcavo-convex portion 24 a on the surface thereof. The surface of thereflecting film 20 also has a concavo-convex portion due to theconcavo-convex portion 24 a.

Since reflected light is scattered due to such a concavo-convex portion,it is possible to prevent the reflected light from being incident fromthe outside and to thus display images with a wide viewing angle.

Also, the color filter 22 (the red colored layer 22R in FIG. 3( b))extending over the reflective display region R and the transmissivedisplay region T is provided on the reflecting film 20 in the reflectivedisplay region R and on the substrate main body 10A positioned in thetransmissive display region T. Here, the edge of the colored layer 22Ris surrounded by a black matrix BM composed of chromium or the like. Theboundaries of the respective dot regions D1, D2, and D3 are formed bythe black matrix BM (refer to FIG. 3( a)).

Furthermore, an insulating film 26 can be formed on the color filter 22so as to correspond to the reflective display region R. That is, theinsulating film 26 is selectively formed above the reflecting film 20,with the color filter 22 therebetween. The thickness of the liquidcrystal layer 50 in the reflective display region R is different fromthe thickness of the liquid crystal layer 50 in the transmissive displayregion T due to the formation of the insulating film 26. The insulatingfilm 26 is made of an organic film, such as an acryl resin of athickness of 0.5 to 2.5 μm, and has a tilted surface so that thethickness thereof can continuously change around the boundary betweenthe reflective display region R and the transmissive display region T.The thickness of the liquid crystal layer 50 in a portion where theinsulating film 26 does not exist is about 1 to 5 μm. The thickness ofthe liquid crystal layer 50 in the reflective display region R is abouthalf of the thickness of the liquid crystal layer 50 in the transmissivedisplay region T.

As mentioned above, the insulating film 26 functions as a liquid crystallayer thickness-adjusting layer (a liquid crystal layerthickness-controlling layer) that makes the thickness of the liquidcrystal layer 50 in the reflective display region R different from thethickness of the liquid crystal layer 50 in the transmissive displayregion T. According to the embodiment, since the edge of the flatsurface on the insulating film 26 almost coincides with the edge of thereflecting film 20 (the reflective display region), a part or all of thetilted region of the insulating film 26 is included in the transmissivedisplay region T.

A common electrode 9 made of indium tin oxide ITO) is formed on thesurface of the lower substrate 10 including the surface of theinsulating film 26. An alignment film 27 made of polyimide is formed onthe common electrode 9. The alignment film 27 functions as a verticalalignment film for aligning the liquid crystal molecules in a verticaldirection with respect to the surface thereof. An alignment process suchas rubbing is not performed. On the other hand, in FIG. 3, the commonelectrode 9 is in strips so as to extend in a vertical direction withrespect to the plane of the drawing and is composed of common electrodesin the respective dot regions formed in parallel in a vertical directionwith respect to the plane of the drawing. Also, in the common electrode9, slits 91 obtained by partially cutting the common electrode areformed. Furthermore, according to the present embodiment, the reflectingfilm 20 and the common electrode 9 are separately provided and stacked.However, in the reflective display region R, a reflecting film made of ametal film may be used as a part of the common electrode.

Next, in the upper substrate 25, the pixel electrode 31 in a matrix,which is made of a transparent conductive film such as ITO, and analignment film 33, which is made of polyimide and on which the verticalalignment process is performed like on the lower substrate 10, areformed on a substrate main body 25A made of a light transmissivematerial, such as glass or quartz (on the liquid crystal layer side ofthe substrate main body 25A). Protrusions 28 that protrude from theinternal surface of the pixel electrode 31 to the inside of the liquidcrystal layer 50 are formed on the internal surface side of the uppersubstrate 25 in the dot region. Also, a protrusion 58 that protrudesfrom the internal surface of the substrate to the inside of the liquidcrystal layer 50 is provided outside the dot region.

A retardation plate 18 and a polarizer 19 are formed on the externalsurface side (the side opposite to the surface on which the liquidcrystal layer 50 is provided) of the lower substrate 10. A retardationplate 16 and a polarizer 17 are formed on the external surface side ofthe upper substrate 25. Circular polarized light can be incident on theinternal surface side of the substrate (the liquid crystal layer 50side). The retardation plate 18 and the polarizer 19, and theretardation plate 16 and the polarizer 17 constitute circularpolarizers, respectively. The polarizer 17(19) transmits only linearlypolarized light having a polarization axis in a predetermined direction.A λ/4 retardation plate can be used as the retardation plate 16(18). Abacklight 15 that is a light source for the transmissive display isprovided outside the polarizer 19 formed on the lower substrate 10.

In the liquid crystal display device 100 according to the embodiment, inorder to regulate the alignment of the liquid crystal molecules of theliquid crystal layer 50, that is, as means for regulating the directionsin which the liquid crystal molecules that are vertically aligned in aninitial state fall when a voltage is applied between electrodes,protrusions made of a dielectric material are formed on the internalsurface side (the liquid crystal layer side) of the electrodes. In FIG.3, in the inside of the transmissive display region T, the protrusions28 are formed on the internal surface side (the liquid crystal layerside) of the pixel electrode 31 formed in the upper substrate 25.

The protrusions 28 protrude from the internal surface of the substrate(the main surface of the electrode) to the inside of the liquid crystallayer 50 and are in the shape of lines (in strips) in plan view. To bespecific, the height of the protrusions 28 is about 0.5 to 2.5 μm, thatis, almost equal to the thickness of the liquid crystal layer in theregion where the insulating film 26 is not formed (that is, thereflective display region R). Also, the protrusions 28 include a surface(including a slowly curved shape) tilted at a predetermined angle withrespect to the internal surface of the substrate (the main surface ofthe electrode).

Furthermore, the protrusion 58 can be formed outside the dot region. Theprotrusion 58 has a height almost equal to the heights of theprotrusions 28 (in the drawing, the heights of the protrusions lookdifferent from each other for clarity) and is a cone or a polypyramidhaving a tilted surface. In this case, the protrusion 58 regulates thedirections in which the liquid crystal molecules LC fall and, inparticular, is provided in the region (the reflective display region R)where the insulating film 26 is formed so as to be used as means forregulating the distance between the substrates, that is, the cell gap.

On the other hand, in the common electrode 9 formed on the internalsurface side of the lower substrate 10, the slits 91 obtained bypartially cutting the common electrode 9 are formed. By providing theslits 91, a distorted electric field can be generated between therespective electrodes 9 and 31 in the region where the slits are formed.The directions in which the liquid crystal molecules vertically alignedin an initial state fall when a voltage is applied are regulated by thedistorted electric field. As illustrated in FIG. 3( a), the slits 91 inthe form of lines, which are formed in the common electrode 9, alternatewith the protrusions 28 formed in the pixel electrode 31 in plan view.As a result, it is possible to alternately regulate the directions inwhich the liquid crystal molecules LC fall between the slits 91 and theprotrusions 28.

According to the liquid crystal display device 100 having the abovestructure, it can be possible to obtain the following effects. First, inthe liquid crystal display device 100 according to the presentembodiment, since it is possible to reduce the thickness of the liquidcrystal layer 50 in the reflective display region R to half of thethickness of the liquid crystal layer 50 in the transmissive displayregion T by forming the insulating film 26 in the reflective displayregion R, it is possible to make the birefringence retardation thatcontributes to the reflective display almost equal to the birefringenceretardation that contributes to the transmissive display and to thusimprove the contrast.

In general, when a voltage is applied to the liquid crystal moleculeshaving negative dielectric anisotropy, which are aligned on a verticalalignment film on which a rubbing process is not performed, since thedirections in which the liquid crystal molecules fall are not regulated,the liquid crystal molecules fall in random directions to thus causeinferior alignment. However, according to the embodiment, since theprotrusions 28 are formed on the internal surface side of the pixelelectrode 31 and the slits 91 are formed in the common electrode 9 so asto be positioned between the adjacent protrusions 28 among theprotrusion 28 formed in the pixel electrode 31, the alignment of theliquid crystal molecules is regulated by the tilted surfaces of theprotrusions 28 and/or by the distorted electric field caused by theslits 91. Therefore, the directions in which the liquid crystalmolecules vertically aligned in an initial state fall when a voltage isapplied are regulated. As a result, it is possible to prevent thegeneration of disclinations caused by the inferior alignment of theliquid crystal molecules and to thus obtain high quality display inwhich afterimages caused by the generation of the disclinations or spotsobserved in the oblique direction are rarely generated.

According to the embodiment, the protrusions 28 can be selectivelyprovided in the transmissive display region T. Considering that it ispossible to prevent the generation of disclinations and to improve thedisplay characteristics by regulating the directions in which the liquidcrystal molecules fall, the protrusions 28 are preferably formed in thereflective display region R as well as in the transmissive displayregion T. Since the luminosity is higher in the transmissive mode thanin the reflective mode, the protrusions are preferably formed in thetransmissive display region T. The above effects can be obtained by thestructure in which the protrusions are formed in the reflective displayregion R.

Furthermore, the protrusions 28 are formed in the transmissive region Tin order to regulate the alignment of the liquid crystal molecules. Atthe same time, the protrusion 58 is formed outside the dot region.Therefore, it is possible to regulate the directions in which the liquidcrystal molecules fall around the protrusion 58. As a result, it ispossible to prevent the occurrence of inferior alignment of the liquidcrystal molecules at the edge of the dot region due to the inferioralignment, which is generated outside the dot region. Furthermore, sincethe protrusion 58 formed outside the dot region is formed in the region(the reflective display region) in which the insulating film 26 isprovided, it is possible to use the protrusion 58 as means forregulating the cell gap. That is, since the thickness of the liquidcrystal layer is small in the region where the insulating film 26 isformed, the protrusion 58 formed in the region can be used as the liquidcrystal layer thickness-regulating means for maintaining the cell gap tohave a predetermined thickness.

Therefore, in the liquid crystal display device 100 according to theembodiment, it is possible to display highly visible images with highcontrast by a simple structure without additionally providing spacers,unlike in the conventional art, by preferably regulating the directionsin which the liquid crystal molecules fall and by letting at least oneof the means for regulating the directions in which the liquid crystalmolecules fall have the function of regulating the cell gap.

A liquid crystal display device according to a second embodiment willnow be described with reference to the drawings. FIG. 4 is a schematicview illustrating the planar structure (a) and the sectional structure(b) of the liquid crystal display device 200 according to the secondembodiment corresponding to FIG. 3 according to the first embodiment.The structure of the liquid crystal display device 200 according to thesecond embodiment is almost identical with the structure of the liquidcrystal display device 100 illustrated in FIG. 3 excluding that thestructures of the protrusions and the slits vary. Therefore, descriptionof the same members denoted by the reference numerals of FIG. 3 will beomitted.

In the liquid crystal display device 200 according to the secondembodiment, unlike in the liquid crystal display device 100 according tothe first embodiment, the protrusions 28 are formed on the commonelectrode 9 of the lower substrate 10 in the transmissive display regionT. On the other hand, the protrusion 58 is formed on the commonelectrode 9 of the lower substrate 10 outside the dot region. Also,unlike in the first embodiment, the protrusions 28 are cones orpolypyramids. Like in the first embodiment, the protrusion 58 isprovided in the region where the insulating film 26 is formed. On theother hand, slits 32 are formed in the pixel electrode 31 of the uppersubstrate 25. In this case, the slits 32 are formed so as to surroundthe protrusions 28 in plan view.

According to the liquid crystal display device 200 of the secondembodiment, it is possible to obtain the same effects as the liquidcrystal display device according to the first embodiment. In otherwords, the protrusions 28 formed in the transmissive display region Tfunction as means for regulating the directions in which the liquidcrystal molecules fall. On the other hand, the protrusion 58 formed onthe insulating film 26 outside the dot region functions as means forregulating the directions in which the liquid crystal molecules fall andthe cell gap. Therefore, since the liquid crystal display device 200includes the protrusions 28 and the electrode slits 32 as the device forpreferably regulating the directions in which the liquid crystalmolecules fall, it is possible to prevent the generation ofdisclinations caused by inferior alignment of the liquid crystalmolecules and to thus obtain high quality display in which afterimagescaused by the generation of the disclinations or spots observed in theoblique direction are rarely generated. Also, it is possible to displayhighly visible images with high contrast by a simple structure withoutadditionally providing the spacers by letting the protrusion 58 formedon the insulating film 26 have the function of regulating the cell gapamong the means for regulating the directions in which the liquidcrystal molecules fall.

A liquid crystal display device according to a third embodiment will nowbe described with reference to the drawings. FIG. 5 is a schematic viewillustrating the planar structure (a) and the sectional structure (b) ofthe liquid crystal display device 300 according to the third embodimentcorresponding to FIG. 4 according to the second embodiment. Thestructure of the liquid crystal display device 300 according to thethird embodiment is almost identical with the structure of the liquidcrystal display device 200 illustrated in FIG. 4 excluding that thepositions in which the protrusions are formed are different from thepositions according to the second embodiment. Therefore, description ofthe same members denoted by the reference numerals of FIG. 4 will beomitted.

In the liquid crystal display device 300 according to the thirdembodiment, like in the liquid crystal display device 200 according tothe second embodiment, the protrusions 28 are formed on the commonelectrode 9 of the lower substrate 10 in the transmissive display regionT. On the other hand, unlike in the liquid crystal display device 200,no protrusions are formed outside the dot region. However, protrusions29 are formed in the reflective display region R in the dot region. Theprotrusions 29 have the function of regulating the cell gap. Also, likethe protrusions 28, the protrusions 29 are generally shaped as cones orpolypyramids. On the other hand, the slits 32 are formed in the pixelelectrode 31 of the upper substrate 25. In this case, the slits 32 areformed so as to surround the protrusions 28 and 29 in plan view.

According to the liquid crystal display device 300 of the thirdembodiment, it is possible to obtain the same effects as those of thefirst and second embodiments. That is, the protrusions 28 formed in thetransmissive display region T and the protrusions 29 formed in thereflective display region R function as means for regulating thedirections in which the liquid crystal molecules fall. In particular,the protrusions 29 formed on the insulating film 26 in the reflectivedisplay region R function as means for regulating the cell gap as wellas the directions in which the liquid crystal molecules fall. Therefore,since the liquid crystal display device 300 includes the protrusions 28and 29 and the electrode slits 32 as means for preferably regulating thedirections in which the liquid crystal molecules fall, it is possible toprevent the generation of disclinations caused by inferior alignment ofthe liquid crystal molecules and to thus obtain high quality display inwhich afterimages caused by the generation of the disclinations or spotsobserved in the oblique direction are rarely generated. Also, it ispossible to display highly visible images with high contrast by a simplestructure without additionally providing the spacers by letting theprotrusions 29 formed on the insulating film 26 in the reflectivedisplay region R have the function of regulating the cell gap among themeans for regulating the directions in which the liquid crystalmolecules fall.

Also, the protrusions 29 formed in the reflective display region Rcontact the opposite substrate in order to regulate the cell gap.Therefore, an alignment regulating force of the liquid crystal moleculesis weaker than that of the protrusions 28. Therefore, as illustrated ina liquid crystal display device 400 of FIG. 6, it is possible toincrease the alignment regulating force of the liquid crystal moleculescompared with that of the cone-shaped protrusions by forming protrusions29 a in strips in the reflective display region R in order to regulatethe cell gap. In other words, in this case, since the tilt angle of thetilted surface is larger than that of the cone-shaped protrusions, it ispossible to improve the alignment regulating force of the liquid crystalmolecules.

A liquid crystal display device according to a fourth embodiment willnow be described with reference to the drawings. FIG. 7 is a schematicview illustrating the planar structure (a) and the sectional structure(b) of the liquid crystal display device 500 according to the fourthembodiment corresponding to FIG. 3 according to the first embodiment.The structure of the liquid crystal display device 500 according to thefourth embodiment is almost identical with the structure of the liquidcrystal display device 100 illustrated in FIG. 3 excluding that thepositions in which the protrusions and the slits are formed and thestructures of the protrusions and the slits are different from thepositions and the structure according to the first embodiment.Therefore, description of the same members denoted by the referencenumerals of FIG. 3 will be omitted.

In the liquid crystal display device 500 according to the fourthembodiment, like in the liquid crystal display device 100 according tothe first embodiment, the protrusions 28 are formed on the pixelelectrode 31 of the upper substrate 25 in the transmissive displayregion T. On the other hand, the protrusion 58 is formed outside the dotregion of the upper substrate 25 in the position where the insulatingfilm 26 is formed. Like in the first embodiment, the protrusion 58 hasthe function of regulating the cell gap. Also, unlike in the firstembodiment, the protrusions 28 are the cones or the polypyramids. On theother hand, the slits 91 are formed in the common electrode 9 of thelower substrate 10. In this case, the slits 91 are formed so as tosurround the cone-shaped or polypyramid-shaped protrusions 28 in planview.

According to the liquid crystal display device 500 of the fourthembodiment, it is possible to obtain the same effects as those of thefirst to third embodiments. In other words, the protrusions 28 formed inthe transmissive display region T function as means for regulating thedirections in which the liquid crystal molecules fall. On the otherhand, the protrusion 58 provided outside the dot region in the positionwhere the insulating film 26 is formed functions as the device forregulating the cell gap as well as the directions in which the liquidcrystal molecules fall. Therefore, since the liquid crystal displaydevice 500 includes the protrusions 28 and the electrode slits 32 as themeans for preferably regulating the directions in which the liquidcrystal molecules fall, it is possible to prevent the generation ofdisclinations caused by inferior alignment of the liquid crystalmolecules and to thus obtain high quality display in which afterimagescaused by the generation of the disclinations or spots observed in theoblique direction are rarely generated. Also, it is possible to displayhighly visible images with high contrast by a simple structure withoutadditionally providing the spacers by letting the protrusion 58 providedoutside the dot region in a position corresponding to the position inwhich the insulating film 26 is formed have the function of regulatingthe cell gap among the means for regulating the directions in which theliquid crystal molecules fall.

A liquid crystal display device according to a fifth embodiment will nowbe described with reference to the drawings. FIG. 8 is a schematic viewillustrating the planar structure (a) and the sectional structure (b) ofthe liquid crystal display device 600 according to the fifth embodimentcorresponding to corresponding to FIG. 7 according to the fourthembodiment. The structure of the liquid crystal display device 600according to the fifth embodiment is almost identical with the structureof the liquid crystal display device 500 illustrated in FIG. 7 excludingthat the positions in which the protrusions are formed are differentfrom the positions according to the fourth embodiment. Therefore,description of the same members denoted by the reference numerals ofFIG. 7 will be omitted.

In the liquid crystal display device 600 according to the fifthembodiment, like in the liquid crystal display device 500 according tothe fourth embodiment, the protrusions 28 are formed on the pixelelectrode 31 of the upper substrate 25 in the transmissive displayregion T. On the other hand, unlike in the liquid crystal display device500, no protrusions are formed outside the dot region. However, theprotrusions 29 are formed in the reflective display region R in the dotregion. The protrusions 29 have the function of regulating the cell gap.Also, like the protrusions 28, the protrusions 29 are the cones or thepolypyramids. On the other hand, the slits 91 are formed in the commonelectrode 9 of the lower substrate 10. In this case, the slits 91 areformed so as to surround the protrusions 28 and 29 in plan view.

According to the liquid crystal display device 600 of the fifthembodiment, it is possible to obtain the same effects as those of thefirst to fourth embodiments. That is, the protrusions 28 formed in thetransmissive display region T and the protrusions 29 formed in thereflective display region R function as a device for regulating thedirections in which the liquid crystal molecules fall. In particular,the protrusions 29 provided in the position corresponding to theposition in which the insulating film 26 is formed in the reflectivedisplay region R function as means for regulating the cell gap as wellas the directions in which the liquid crystal molecules fall. Therefore,since the liquid crystal display device 600 includes the protrusions 28and 29 and the electrode slits 91 as the device for preferablyregulating the directions in which the liquid crystal molecules fall, itis possible to prevent the generation of disclinations caused byinferior alignment of the liquid crystal molecules and to thus obtainhigh quality display in which afterimages caused by the generation ofthe disclinations or spots observed in the oblique direction are rarelygenerated. Also, it is possible to display highly visible images withhigh contrast by a simple structure without additionally providing thespacers by letting the protrusions 29 provided in the positioncorresponding to the position in which the insulating film 26 is formedin the reflective display region R have the function of regulating thecell gap among the means for regulating the directions in which theliquid crystal molecules fall.

Also, the protrusions 29 formed in the reflective display region Rcontact the opposite substrate in order to regulate the cell gap.Therefore, the alignment regulating force of the liquid crystalmolecules is weaker than that of the protrusions 28 in the transmissivedisplay region T. Therefore, it is possible to improve the alignmentregulating force of the liquid crystal molecules than that of thecone-shaped or polypyramid-shaped protrusions by forming protrusions 29a in strips in the reflective display region R. In other words, in thiscase, since the tilt angle of the tilted surface is larger than that ofthe cone-shaped protrusions, it is possible to improve the alignmentregulating force of the liquid crystal molecules.

A detailed example of an electronic apparatus including the liquidcrystal display device according to the embodiment of the invention willnow be described.

FIG. 9 is a perspective view illustrating an example of a mobiletelephone. In FIG. 9, reference numerals 1000 and 1001 denote a mobiletelephone main body and a display portion using the liquid crystaldisplay device, respectively. Since such an electronic apparatusincludes a display portion using the liquid crystal display deviceaccording to the present embodiment, it is possible to realize anelectronic apparatus having a bright liquid crystal display portion withhigh contrast and a wide viewing angle, which is not dependent on useenvironments.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it should be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention. For example, according to the above embodiments, theretardation plate is a single plate, however, may be a stacked substanceobtained by stacking a ½ wavelength plate and a ¼ wavelength plate. Thestacked substance functions as a wideband circular polarizer and canmake black display achromatic. Also, the shapes of the protrusions andthe electrode slits formed in the present embodiments are not limited tothe structures of the above embodiments. The protrusions and theelectrode slits may have any shapes suitable for regulating thedirections in which the vertically aligned liquid crystal moleculesfall. Also, according to the above respective embodiments, theinsulating film 26 is formed in the lower substrate 10. However, theinsulating film may be formed in the upper substrate 25. Furthermore,according to the above respective embodiments, the TFD is used as aswitching element. However, a thin film transistor (TFT) instead of theTFD may be used as the switching element.

While this invention has been described in conjunction with the specificembodiments thereof, it is evident that many alternatives,modifications, and variations will be apparent to those skilled in theart. Accordingly, preferred embodiments of the invention as set forthherein are intended to be illustrative, not limiting. There are changesthat may be made without departing from the spirit and scope of theinvention.

1. A liquid crystal display device, comprising: a liquid crystal layerinterposed between a pair of substrates, the liquid crystal layerincluding a liquid crystal having a negative dielectric anisotropy; adot region in which a transmissive display region and a reflectivedisplay region are provided; a liquid crystal layer thickness-adjustinglayer that makes a thickness of the liquid crystal layer in thereflective display region smaller than a thickness of the liquid crystallayer in the transmissive display region, the liquid crystal layerthickness-adjusting layer being formed between at least one substrate ofthe pair of substrates and the liquid crystal layer; a first convexportion made of dielectric material formed in the transmissive region;and a second convex portion that protrudes from an internal surface ofat least one of the substrates to an inside of the liquid crystal layer,and in contact with the other of the substrates, the second convexportion being formed in a region where the liquid crystal layerthickness-adjusting layer is formed outside the dot region.
 2. Theliquid crystal display device according to claim 1, the first convexportion including a surface inclined at an angle with respect to thesurfaces of the substrates.
 3. The liquid crystal display deviceaccording to claim 1, electrodes that drive the liquid crystal beingprovided on the liquid crystal layer sides of the pair of substrates,and the first convex portion being formed on at least one electrode ofthe electrodes facing the liquid crystal layer.
 4. The liquid crystaldisplay device according to claim 3, an alignment film that verticallyaligns the liquid crystal being formed on the convex portions and theinternal surface of the electrodes facing the liquid crystal layer. 5.The liquid crystal display device according to claim 1, circularpolarizers that make circularly polarized light incident on the liquidcrystal layer being provided on sides of the pair of substrates oppositeto the liquid crystal layer, respectively.
 6. The liquid crystal displaydevice according to claim 1, an upper substrate and a lower substratebeing provided as the pair of substrates, a backlight for transmissivedisplay being provided at the side of the lower substrate opposite tothe liquid crystal layer, and a reflective layer selectively formed inthe reflective display region being formed on the side of the lowersubstrate facing the liquid crystal layer.
 7. An electronic apparatus,comprising the liquid crystal display device according to claim 1.